What would you want a zony for? Well, what do you want your Percheron for?
You realize that, it terms of doing genetic damage, you're much more likely to run into problems breeding like to like than you are breeding two very different individuals, right? Ever heard of "hybrid vigor?" It's a real phenomenon, and at the same time, "incestuous" inbreeding is very dangerous. In fact, I just read that the Przewalski's horse is in serious danger of extinction due to inbreeding. Many of the mares are infertile, and there is only a 20% breeding to birth rate, as opposed to a 60% rate in domestic horses. That's the danger of homozygous characteristics, and it's why the European royal families are plagued by hemophilia and why many purebred dogs have serious genetic problems like epilepsy or hip displacia. Or how about HERDA, SCID, CA, and GBED in horses?
So, from your "tampering with nature" standpoint, we did the most harm when we created this homogenous breeds in the first place, and we would have been better off leaving well enough alone. No more domestic animals, guys--you're screwin' stuff up!